Here's how long we have before Earth is uninhabitable

By Eric Berger

Published 6:32 pm, Thursday, November 1, 2012

Photo: AP, HONS

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This artist s impression made available by the European Southern Observatory on Tuesday, Oct. 16, 2012 shows a planet, right, orbiting the star Alpha Centauri B, center, a member of the triple star system that is the closest to Earth. Alpha Centauri A is at left. The Earth's Sun is visible at upper right. Searching across the galaxy for interesting alien worlds, scientists made a surprising discovery: a planet remarkably similar to Earth in a solar system right next door. Other Earth-like planets have been found before, but this one is far closer than previous discoveries. Unfortunately, the planet is way too hot for life, and it s still 25 trillion miles away. (AP Photo/ESO, L. Calcada) less

This artist s impression made available by the European Southern Observatory on Tuesday, Oct. 16, 2012 shows a planet, right, orbiting the star Alpha Centauri B, center, a member of the triple star system that ... more

Photo: AP, HONS

Here's how long we have before Earth is uninhabitable

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The Earth is warming some now, but this is not an article about human-induced climate change.

Regardless of what we do, in a couple of billion years the Earth is going to warm A LOT.

Our Sun, Sol, is a G-class star. It is now about 4.5 billion years old, and in about five billion years it will begin rapidly expanding into what's known as a "red giant." Clever name, that, because the Sun will in fact become a giant red star and eventually expand beyond the Earth's orbit. Everything on the planet will be incinerated.

But in truth, Earth will become unlivable a lot earlier than that, according to a new study.

As the Sun ages, its luminosity will increase, making it become larger and brighter. This process will play out over hundreds of millions of years - so it's not like this is something that will occur during our life times. But it's already at work and will make its effects really felt in about 1 billion years.

Here's what scientists think will happen in about 2 billion years:

Increased temperatures cause increased atmospheric water vapor – a greenhouse gas, the presence of which further increases surface temperatures.

For the next billion years or so this might increase cloud cover, cooling temperatures modestly.

Eventually more energy from the Sun will win out, and higher temperatures lead to increased weathering of silicate rocks, drawing down more carbon from the atmosphere.

Carbon is normally recycled though plate tectonics; however, increasing water loss eventually halts plate tectonics.

This in turn decreases oxygen production, which, with continued consumption by biota and by oxidation of organic carbon in sedimentary rocks, leads to a steady decline in atmospheric oxygen to zero over a few million years.

The end of animal life would occur a few million years after the end of plant life.

Large endotherms (mammals, birds) would likely be the first group to become extinct due to their higher oxygen requirements.

Fish, amphibians, reptiles would be able to survive for longer, but eventually the oceans will evaporate.

The last life on Earth, in about 2.8 billion years, will be single-celled, heat-loving organisms in isolated pools of hot, salty water.

So how's that for an uplifting message?

Unlike climate change, largely driven by greenhouse gases, this solar warming scenario in a couple of billion years is unstoppable. However, there is a silver lining. If the human species manages to survive its myriad other threats - asteroids, increasingly sophisticated biological weapons - we're beginning to find a lot of planets around a lot of other worlds.

In the last 100 years we've gone from a 12-second flight by the Wright brothers to living in space. Given that there are a lot of other worlds, humans will eventually have the capacity to reach them in plenty of time.